Grid support for fluidized solids vessels



June 3, 1958 1-1. c. NORTH GRID SUPPORT FOR FLUIDIZED SOLIDS VESSELSFiled Dec. 14, 1955 mmawt i. H mmzwt 9% MSEA N Inventor I Howard C.North By 1 M Attorney atent 2,836,902 Patented June 3, 1958 fiice GRIDSUPPORT FOR FLUIDIZED SOLIDS VESSELS Howard C. North, Westfield, N. J.,assignor to Esso Research and Engineering Company, a corporation ofDelaware Application December 14, 1955, Serial N 0. 552,997

2 Claims. (Cl. 34-57) This invention relates to an improved apparatusfor contacting fluidized solids with gasiform fluids. The inventionpertains more particularly to a vessel wherein finely divided solids,either catalytic or non-catalytic, are fluidized and treated or reactedwith liquid or gaseous fluids, for example, for regenerative and/ orheat production purposes at temperatures above about 900 F. Thisinvention proposes an improved grid or gas distributor plate design forsupporting, and uniformly distributing a gasiform reactant throughout, ahigh temperature fluidized solids bed within a reaction vessel.

This invention will find use in various fluidized solids processes suchas ore roasting, drying of wet solids, coal carbonization or burning forpower generation, shale retorting, catalytic cracking of gas oils,reforming of heavy naphthas, and coking of heavy oils. It has particularutility in the burning of carbon-containing solids wherein relativelyhigh temperatures are encountered, such as in the regeneration of spentcracking or hydroforming catalyst. It is especially adapted to thepartial burning of particulate fluid coke used as a heat carrier in ahydrocarbon oil fluid coking process, for supplying heated solids to thereaction zone, and will be described in relation to this fluid cokingprocess.

In the fluid coking process, as used in the petroleum industry, a heavyoil-usually a low value residual oil, shale oil, asphalt, etc., isconverted by pyrolysis to relatively lighter hydrocarbons and coke bycontact with fluidized finely divided heat carrying solids maintained ata coking temperature in the range of 850 to 1600 F., or above. The cokeproduced by the pyrolysis deposits on the fluidized solids, layer bylayer, and becomes a part thereof. The heat carrying solids normallyused are coke particles produced by the process, but other types ofsolids can be used such as sand, spent catalyst, and metal particles.

Heat is supplied to the coking zone by withdrawing carbon containingsolids from the coking zone and partially burning them as a fluidizedbed in a burning zone, whereby their temperature is raised 100 to 400 F.above the coking temperature. The solids so heated are then returned tothe coking zone.

This invention is concerned with an improved grid design for supportingthe fluid bed within the burning zone, and for uniformly distributingthe combustion air throughout the bed.

In fluidized solids vessels, it has been found desirable to provide agrid or foraminous plate to uniformly disperse the fluidizing gas orgasiform reactant throughout the bed. In early designs, this gasdistributing means was placed within the bed and operated at thetemperature ofv the bed. At high temperatures this required specialalloys, usually non-weldable, to be used to resist the severe erosiveand corrosive conditions. In later designs, the grid was utilized toalso support the bed so that the fluidizing gas, which is usually at alower temperature than the temperature of the bed, when passing upthrough the grid would cool the grid. The perforations or open ings inthe grid were designed to create a pressure drop (gas velocity) over thegrid sufliciently high to prevent any significant amount of thefluidized solids from passing down through the grid. By this means, itwas found, for example, in the regeneration of catalyst from a gas oilcatalytic cracking process, that the grid temperature could bemaintained below 600 F. This permitted carbon steels to be used. Also,it became the practice to internally insulate the vessels to maintainlow vessel shell temperature, e. g., about 300 to 500 F.

In the design Where the grid supports the fluid bed, it was conventionalpractice to support the grid on a series of clips or lugs around thecircumference of the vessel, the clips being welded to the shell of thevessel. The grid was bolted to the clips with the bolt holes beingslotted to permit thermal movement between the grid and the relativelycool metal shell of the vessel. it was not feasible to combine theseparate support clips into a continuous support ring because at hightemperatures, undesirable high thermal stresses would occur, both in thering and in the vessel shell, particularly with internally insulatedvessels.

Because the clips were separate from one another, a grid sealing devicehas been necessary to prevent air or fluidized solids from passingthrough the spaces between the clips and the periphery of the grid, andalso from passing through the vessel insulation. To accomplish this, athin flexible membrane of stainless steel, Welded to a vapor stopattached to the vessel shell and extending over and fastened to thegrid, has been used. The grid sealing device in one design had aninverted V shape in cross section. A positive mechanical seal was thusformed which prevented any leakage around the grid or through clearancesthat existed in the grid support bolt holes.

This grid seal type of arrangement, besides being cumbersome andexpensive, has proved to be somewhat unsatisfactory. It is amenable toerosion and while accommodating horizontal movement between the grid andthe vessel shell, it will accommodate only very little vertical movementwithout rupture. Because by necessity this grid seal arrangement isthin, it will not stand a very high pressure diiferential over the grid,which pressure diflerential in fluid coke burners may be considerable.

The present invention proposes an improved grid and grid sealingarrangement which overcomes these and other difliculties. This novelgrid design adequately allows for diiferences in thermal expansion andcontraction in the equipment, while providing support for the grid andpreventing passage of gases around the periphery of the grid.

In the drawings:

Figure I illustrates a fluidized solids vessel containing a gridarrangement designed in accordance with the teachings of this invention.Figure ll illustrates an alternative embodiment of this invention.

In brief compass, this invention proposes a grid in the lower portion ofa fluidized solids vessel in horizontal spaced relation to the Walls ofthe vessel, for uniformly distributing a gasiform medium throughout afluidized bed of high temperature, particulate solids contained therein,and for supporting the bed; in combination with 'an in-part verticallydisposed gas impervious skirt or definite upper level 3.. For purposesof illustration, the fluid bed may comprise fluid. coke particles beingoxidatively reheated'to supply heated solids to a hydrocarbonoilfluidcoking vessel. Cool solids from the fluid coking .vessel arecirculated andintroduced into burning" vessel 1 by line 4, and rehe'ated solids at a temperature of 100 to 400 F.'above thecoking temperatureare circulated to the coking zone via line 5, in a manner known by theart.

Air is admitted to the base of the burner vessel 1,

which preferably has a cone bottom, by line 6 and fiuidizes and burnsthe coke within the vessel tomaintain a temperature therein of about 900to 2000? F. Flue gases from the burner are vented overhead via line-7after having entrained solids removed in cyclone system 8.

Accordingto this invention, the fluid bed 2 is supported, and-thecombustion air is uniformly distributed throughout" the fluid bed, by agasiform' distributing" means, i. e.,. a perforated circular-grid 9. Thegrid is horizontally spaced from the vessel walls, usually 1 V 'to 3inches, suflicient to permit thermal expansion'of the sufficiently longto keep thermal bending-stresses plus pressure stresses to an allowablevalue. Thelen'gth and thickness of the. skirt are selected depending onthe specific'design conditions, the actual dimensions being such thatthe combined pressure and bending stress is 7 within the allowable forthe material used." It is essential that the skirt have a minimum lengthdetermined by temperature gradient over the skirt, D=diameter of theskirt, l=thickness of the skirt, L=length of the skirt, and T :thetemperature of the skirt. For most vessels, the vertical height of theskirt is at least 18 to 30 inches. To provide a reasonably smooth .andlow value of the temperature gradient over the skirt, it is alsoessential that insulationll within the vessel extends part way, usually18' to 24 inches, along the skirt from the vessel walls, as shown. Thisreduces the bending stresses in the skirt.

Another important feature of this'designi is that the skirt is welded tothe vessel shell; preferably with a continuous full penetration weld, toprevent passage of air and fluidized solids around the skirt. The-.skirt can also be welded to the grid, although other fasteningarrangements can be used here. i

In vessels over about 10 ftfin diameter, grid 9 is slightly dished inorder to give it the membrane strength associated with curved surfaces,thus making it selfsupporting and eliminating the framework of beamsrequired to support flat grids. A downward, rather than an upward, dishis employed toreduce the volume of 'waste (unoccupied) space belowthergrid.

The amount of dish in the grid (radiusof curvature) represents acompromise between mechanical and process considerations. If the radiusof curvature is too small, the depth of the dish causes asignificantditference in the hydrostatic head of the fluidized solids acting in thecenter of the grid, compared with points near'its 4 supportthe mass ofsolids'in an unfluidized condition at the operating temperatures. 7

Figure II illustrates another embodiment of the invention wherein thegrid, instead of being dependent or hanging from the skirt, issuperposed on the skirt.- The design of Figure I is preferred: becauseit permits place-' ment of the grid lower down in the vessel space belowthe grid is minimized.

whereby waste.

In Figure II, dished grid is supported by a vertical continuous circularring or skirt 21.: The skirt initiates from and is welded to the conebottom of vessell22. As is essential, refractory lining or insu1ation23'of the vessel extends part way over the'skir't to create a uniformtemperature differential.

It will be appreciated by those skilled in the art that this grid andgrid support and seal arrangement may be used in multiple forms, thusone skirt can support two or more grids in vertical spacedarrangementpor; a

plurality of concentric'skirts can be used 1to supportla plurality ofvertically'jspiaced grids; It is desirablein some applications to use aplurality or series of grids to permit a wide variation in operatingconditions; For example, two grids can be used with the lower one havinga lesser free area or smaller perforations; In this way,

' dual grid design, some of the ,air during normal ioperaedge. This willcause a greater air flow through the edge normally a condition where thegrid is called upon to protected by Letters Patent is with reference toa'fluid coke burning-vessel, when the air rate. is normal, the coke bed'will-be' supported on the ,upper grid having the larger openings. Atlow air.

rates or minimum capacity, when thejamo untof air passing through theupper grid is not suflicient to prevent coke from back-flowing throughthe grid, the coke bedwill be supported on the lowergrid having thesmallerperforations or openings. -To otfset high pressure drops in thistion can beadmitted between the grids; g

The following specific example will serve to make this invention clear.The example describes .a burning vessel, wherein fluid coke front "ahydrocarbon oil'fluid coking process having a particle size in the range,of about 40 to 800 microns is partially burned at a'temperature'ofabout 1125 F. V J; 1.

Example p Temperature, F

Vessel shell Internal h 7 7 1125 Pressure, p. s. i. g I 12' Air rate 300F., MM std. cu. f t./SD (dry) 12.7 Coke rate to burner 950 R, tons/miniV 4.3 Coke burning rate, lbs./hr V 3500 Coke hold up, tons 21' Beddensity, lbs/cu. ft j. 4 8 Gas velocity in bed, ft./sec i '2 .8 Internalvessel diameter, ft: I L

Shell -i. 5 12,5 Vessel liner f 11.75 Griddiameter, ft 7 M 111.5 Gridthickness, inches u 0.5 Radius of curvature of grid, ft 7 25 Free areaof grid, percent 0.5 AP over grid,p. s. i.: V

Normal 1 r 7 Short time 7 7 p 1 1 Total height of skirt, inches; 7: 24

Having described this invention, what -is'sou ght tobe following claims.7 7 What is'claimedis:

1. In an'apparatus for contacting solids and gases-ab temperatures'aboveabout 900 F. which comprises a] vertically disposed circular vessel,outlet means in'the 1 7 upper portion for removing gases, gas inletmeans in a qit t e; 1 C rb n st e succinctly set forth in the the bottomportion, a foraminous plate positioned within the lower portion of saidvessel and adapted to support a bed of fluidized solids thereon, saidplate being in horizontally spaced relationship to the walls of saidvessel, and particle outlet means extending beneath said plate, theimprovement which comprises employing a downwardly dished foraminousplate supported from above by an in-part vertically disposed, gasimpervious, circular support, said support being attached to the Wallsof said vessel only in the region of the upper end of said support, saidsupport being further characterized as extending downwardly for themajor portion of its length and inwardly away from said vessel walls inspaced relationship thereto, its lower end terminating at andencompassing said plate, whereby gas from beneath said plate is deniedpassage around the periphery of said plate, and the volume of reactorspace below said plate and solids bed is reduced in amount.

2. The improvement of claim 1 wherein said circular support is at leastin part insulated.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN AN APPARATUS FOR CONTACTING SOLIDS AND GASES AT TEMPERATURES ABOVEABOUT 900*F. WHICH COMPRISES A VERTICALLY DISPOSED CIRCULAR VESSEL,OUTLET MEANS IN THE THE BOTTOM PORTION, A FORAMINOUS PLATE POSITIONEDWITHIN THE LOWER PORTION, A FORAMINUOS PLATE POSITIONED WITHIN A BED OFFLUIDIZED SOLIDS THEREON, SAID PLATE BEING IN HORIZONTALLY SPACEDRELATIONSHIP TO THE WALLS OF SAID VESSEL, AND PARTICLE OUTLET MEANSEXTENDING BENEATH SAID PLATE, THE IMPROVEMENT WHICH COMPRISES EMPLOYINGA DOWNWARDLY DISHED FORAMINOUS PLATE SUPPORTED FROM ABOVE BY AN IN-PARTVERTICALLY DISPOSED, GAS IMPERVIOUS, CIRCULAR SUPPORT, SAID SUPPORTBEING ATTACHED TO THE WALLS OF SAID VESSEL ONLY IN THE REGION OF THEUPPER END OF SAID SUPPORT, SAID SUPPORT BEING FURTHER CHARACTERIZED ASEXTENDING DOWNWARDLY FOR THE MAJOR PORTION OF ITS LENGTH AND INWARDLYAWAY FROM SAID VESSEL WALLS IN SPACED RELATIONSHIP THERETO, ITS LOWEREND TERMINATING AT AND ENCOMPASSING SAID PLATE, WHEREBY GAS FROM BENEATHSAID PLATE IS DENIED PASSAGE AROUND THE PERIPHERY OF SAID PLATE, AND THEVOLUME OF REACTOR SPACE BELOW SAID PLATE AND SOLIDS BED IS REDUCED INAMOUNT.